After much hacking, I realise that I have to create a tiny Template in order to use CodeBlock to render code.
Removed incorrect code in preparation for changing gears a little.
I’ve learned a lot about Liquid so far.
Now we stop bad characters from getting in to Liquid tag parameters.
Identified the issue I opened with Shopify/liquid
Removed an obsolete test
Fixed a broken test. (The test itself was incorrect.)
Moved some code into a class for future consumption.